Summary of commonly used high-efficiency filter detection methods

As environmental problems become more and more serious, air governance has become a topic of discussion all over the world. The primary issue in the governance of air pollution is the governance of dust (PM2.5). At present, the conventional dust control work is to filter the flue gas, and it is also a large-scale bag filter used in modern industry. This paper focuses on the test effect and method of dust filtration. Sodium Flame: Originated in the United Kingdom, popular in China, and implemented in some European countries in the 1970s and 1990s. The test dust source is monodisperse sodium chloride salt spray.“quantity”It is the brightness of the hydrogen flame in the presence of salt mist. The main instrument is a photometer. The salt water splashes under the agitation of compressed air, and after drying, it forms a tiny salt mist and enters the air duct. Samples were taken before and after the filter, and the salt mist gas sample turned the color of the hydrogen flame blue and increased its brightness. The brightness of the flame is used to judge the salt fog concentration of the air, and the filtration efficiency of the filter to the salt fog is determined based on this. The average diameter of salt spray particles stipulated by the national standard is 0.4mm, but the actual measurement result of existing domestic devices is 0.5mm. The measurement result of the median diameter of the actual test salt spray particles in Europe is 0.65mm. With the popularity of the scanning method, the sodium flame method is no longer used in Europe. The relevant domestic departments are revising the original national standards, and whether to abolish or continue to use the sodium flame method, there is no conclusion between the two opinions. Relevant standards: UK BS3928-1969, Europe Eurovent 4/4, China GB6165-85. Photometer scans: Dust sources are typically polydisperse droplets, such as DOP fumes from Laskin nozzles. Scan the full plane of the filter for leak detection using a photometer. This scanning method quickly and accurately finds filter leaks. Since the dust source is a polydisperse phase, and the photometer cannot determine the dust particle size, this scanning method gives“Filtration efficiency”Nothing practical. Some manufacturers and users believe that as long as the quality and specifications of the filter paper are strictly controlled, the efficiency of the filter has been determined, so the quality of the filter can be guaranteed by only scanning for the purpose of leak detection. There is no corresponding standard for the method of photometer scanning leak detection, but this method is very effective for the quality control of the production process, and the testing equipment used is relatively simple, so some manufacturers currently use this method. Photometric scanning test benches can easily be converted to counting scanning benches, and a laser particle counter can be purchased for some money. DOP Law: Originated in the United States, internationally accepted, China has never implemented it. The test dust source was 0.3mm droplets of monodisperse DOP (a common plasticizer in the plastics industry).“quantity”is the turbidity of the DOP-containing air. The instrument for measuring dust is a photometer. The turbidity difference of the gas sample is used to determine the filtration efficiency of the filter for DOP particles. The DOP liquid is heated into steam, and the steam is condensed into tiny droplets under certain conditions. After removing the oversized and undersized droplets, the particles of about 0.3mm are left, and the misty DOP enters the air duct. Measure the turbidity of the gas samples before and after the filter, and judge the filtration efficiency of the filter for 0.3mm dust. The DOP method has a history of more than 50 years, and this method used to be the most commonly used method for measuring high efficiency filters in the world. In the early days, it was considered that the filter was the most difficult to filter the dust of 0.3mm, so it was stipulated that the high-efficiency filter should be measured with 0.3mm dust. DOP contains a benzene ring, which is suspected to be carcinogenic, so many laboratories switch to alternatives with similar properties but no benzene ring, such as DOS, but the test method still claims“DOP method”. By changing the dust generation parameters, DOP droplets of other particle sizes can be obtained. So there is the 0.1mm DOP method for measuring ultra-high efficiency filters in Europe and the United States 20 years ago, and sometimes the measuring instrument is also changed to a condensation nuclear laser particle counter. Some foreign manufacturers have marked the filtration efficiency of 0.05mm or 0.03mm DOP, which are unconventional and unscientific in business. The DOP method for measuring high efficiency filters is also called“Hot DOP method”. corresponding to this“Cold DOP”Refers to the polydisperse DOP dust produced by the Laskin nozzle (compressed air bubbles in the liquid, splashing to produce foggy artificial dust), and cold DOP is often used when scanning filters. Relevant standard: US Military Standard MIL-STD-282. Counting scanning method: common in Europe, similar in the United States, followed by other countries. At present, the mainstream test method for high-efficiency filters in the world.

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